Carotenoids are accessory pigments in photosynthetic microorganisms which function by absorbing light and transferring energy to chlorophyll for photosynthesis. Carotenoid also acts to protect cells from photooxidative damage from oxygen radicals produced during photosynthesis. See generally Spurgeon, et al., The Biochemistry of Plants, Chap. 14 (1980).
Xanthophylls are oxygen-containing carotenoids and are useful as natural coloring agents. Xanthophylls and, in particular, lutein and zeaxanthin, are used as feed supplements for poultry to produce a yellowish color in shanks and egg yolks.
Production of carotenoids by fermentation of microorganisms is known. Farrow, U.S. Pat. No. 3,280,502 (1966), a process for the preparation of lutein is disclosed in which a strain of Chlorella pyrenoidosa is fermented and up to 235 mg of lutein per liter is produced in ninety-six hours. Kathrein, U.S. Pat. No. 2,949,700 (1960) discloses a process for the production of carotenoids by the cultivation of algae of the phyla Chlorophyta, including species of Chlorococcum, Chlorella, and Chlamydomonas. Microbiological production of carotenoids by fungi is also known. For example, see Farrow, U.S. Pat. No. 2,974,044 (1961).
The unicellular green alga Nospongiococcum excentricum produces xanthophylls and has been used as a feed additive to provide color. See, for example, Marusich, et al., Oxycarotenoids in Poultry Pigmentation, Poultry Sci. 49 (6) pp. 1555-1566 (1970).
While N. excentricum and other algae are known for producing carotenoids, known developed and wild type strains of algae do not produce sufficient levels of carotenoids for successful commercial production. Accordingly, there is a need for strains of algae having increased levels of carotenoids and methods for selecting such strains. Additionally, there is a need for methods of fermentation of algae for producing increased yields of carotenoids.